Problem solved by dropping table messages and recreating it with
CREATE TABLE `messages` (
`message_id` int(11) unsigned NOT NULL auto_increment,
`user_id` int(11) unsigned NOT NULL default '0',
`del` tinyint(1) NOT NULL default '0',
`cache_key` varchar(128) NOT NULL default '',
`created` datetime NOT NULL default '0000-00-00 00:00:00',
`idx` int(11) unsigned NOT NULL default '0',
`uid` int(11) unsigned NOT NULL default '0',
`subject` varchar(255) NOT NULL default '',
`from` varchar(255) NOT NULL default '',
`to` varchar(255) NOT NULL default '',
`cc` varchar(255) NOT NULL default '',
`date` datetime NOT NULL default '0000-00-00 00:00:00',
`size` int(11) unsigned NOT NULL default '0',
`headers` text NOT NULL,
`structure` text,
PRIMARY KEY (`message_id`),
KEY `user_id` (`user_id`),
KEY `idx` (`idx`),
KEY `uid` (`uid`),
UNIQUE `uniqueness` (`user_id`, `cache_key`, `uid`)
);